Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, or a monitoring camera, or an image pickup apparatus such as a silver-halide film camera.
Description of the Related Art
In recent years, an image pickup optical system for use in an image pickup apparatus using a solid-state image pickup element is required to have a short total lens length, a wide angle of view, a high zoom ratio, and a high optical characteristic over the entire zoom range. As a zoom lens that satisfies those requirements, a positive-lead type zoom lens in which a lens unit having a positive refractive power is arranged closest to an object side has been known. As the positive-lead type zoom lens, a zoom lens including five lens units as a whole has been known.
In Japanese Patent Application Laid-Open No. 2007-212926, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a fifth lens unit having positive, negative, positive, positive, and positive refractive powers, in which the first lens unit to the fourth lens unit are configured to move for zooming. In the zoom lens, the fourth lens unit is configured to move for focusing. In Japanese Patent Application Laid-Open No. 2007-328306, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a fifth lens unit having positive, negative, positive, positive, and positive or negative refractive powers, in which the second lens unit and the fourth lens unit are configured to move for zooming. In the zoom lens, the fourth lens unit is configured to move for focusing.
In Japanese Patent Application Laid-Open No. 2007-212926 and Japanese Patent Application Laid-Open No. 2007-328306, there is disclosed a five-unit zoom lens of a so-called rear focus type in which the second lens unit is moved to mainly vary magnification, and in which the fourth lens unit corrects an image plane variation accompanying the magnification varying and performs focusing. In general, the zoom lens of the rear focus type has a smaller effective diameter of the first lens unit than that of a zoom lens in which the first lens unit is moved to perform focusing, and is easy to reduce the size of the entire lens system. Moreover, close-up photography is easy. Further, a lens unit having small size and weight is moved, which leads to a requirement of small driving power for the lens unit, ability of rapid focusing, and other such features.
With a change in resolution of the image pickup apparatus from Full HD to 4K, the zoom lens used with the image pickup apparatus is required to be a zoom lens that is compatible with a larger image pickup element and has a high optical characteristic.
In general, in a zoom lens, in order to downsize an entire system of the zoom lens while securing a predetermined zoom ratio, the number of lenses may be reduced while strengthening refractive powers of the lens units forming the zoom lens. However, the zoom lens having such configuration generates a larger amount of various aberrations, and it is difficult to satisfactorily correct the various aberrations. In the positive-lead type five-unit zoom lens described above, in order to obtain the high optical characteristic over the entire zoom range while securing the reduced size of the entire system and a high zoom ratio, it is important to appropriately set respective elements of the zoom lens.
For example, it is important to appropriately set the refractive powers of the lens units, movement loci of the second lens unit and the third lens unit accompanying the zooming, imaging magnifications of the third lens unit and the fourth lens unit, lens configurations of the lens units, and the like. When those configurations are not appropriate, the entire system is increased in size in realizing the high zoom ratio, and variations in various aberrations accompanying the zooming are increased. Accordingly, it is very difficult to obtain the high optical characteristic over the entire zoom range and the entire image plane.